Date: Tue, 12 Oct 2004 08:50:41 -0700 From: Sam Leffler <sam@errno.com> To: Sam <sah@softcardsystems.com> Cc: freebsd-arch@freebsd.org Subject: Re: mbuf w/o pkthdr? Message-ID: <416BFD51.2080805@errno.com> In-Reply-To: <Pine.LNX.4.60.0410121115430.30953@athena> References: <Pine.LNX.4.60.0410121115430.30953@athena>
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Sam wrote: > Hello - > > src/sys/i386/i386/busdma_machdep.c:/^bus_dmamap_load_mbuf/ > prohibits loading an mbuf that does not contain a packet > header. Some drivers use this (xl), some don't (fxp). > > Are all packets supposed to have the M_PKTHDR flag? Why? M_PKTHDR indicates an m_pkthdr structure is present in the mbuf. bus_dmamap_load_mbuf requires this as it gets the packet length from it (instead of walking the mbuf chain or taking it as an argument). Most packets typically have this information (can't think of any interesting cases where it is not be there). Sam
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